1. Field
The present invention relates generally to communication systems, and more specifically to a method and an apparatus for processing shared sub-packets in a communication system.
2. Background
Communication systems have been developed to allow transmission of information signals from an origination station to a physically distinct destination station. In transmitting information signal from the origination station over a communication channel, the information signal is first converted into a form suitable for efficient transmission over the communication channel. Conversion, or modulation, of the information signal involves varying a parameter of a carrier wave in accordance with the information signal in such a way that the spectrum of the resulting modulated carrier is confined within the communication channel bandwidth. At the destination station the original information signal is replicated from the modulated carrier wave received over the communication channel. Such a replication is generally achieved by using an inverse of the modulation process employed by the origination station.
Modulation also facilitates multiple-access, i.e., simultaneous transmission and/or reception, of several signals over a common communication channel. Multiple-access communication systems often include a plurality of remote subscriber units requiring intermittent service of relatively short duration rather than continuous access to the common communication channel. Several multiple-access techniques are known in the art, such as time division multiple-access (TDMA), frequency division multiple-access (FDMA), and amplitude modulation multiple-access (AM). Another type of a multiple-access technique is a code division multiple-access (CDMA) spread spectrum system that conforms to the “TIA/EIA/IS-95 Mobile Station-Base Station Compatibility Standard for Dual-Mode Wide-Band Spread Spectrum Cellular System,” hereinafter referred to as the TIA/EIA/IS-95 standard. The use of CDMA techniques in a multiple-access communication system is disclosed in U.S. Pat. No. 4,901,307, entitled “SPREAD SPECTRUM MULTIPLE-ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS,” and U.S. Pat. No. 5,103,459, entitled “SYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM,” both assigned to the assignee of the present invention.
A multiple-access communication system may be a wireless or wire-line and may carry voice and/or data. An example of a communication system carrying both voice and data is a system in accordance with the TIA/EIA/IS-95 standard, which specifies transmitting voice and data over the communication channel. A method for transmitting data in code channel frames of fixed size is described in detail in U.S. Pat. No. 5,504,773, entitled “METHOD AND APPARATUS FOR THE FORMATTING OF DATA FOR TRANSMISSION”, assigned to the assignee of the present invention. In accordance with the TIA/EIA/MS-95 standard, the data or voice is partitioned into code channel frames that are 20 milliseconds wide with data rates as high as 14.4 Kbps. Additional examples of a communication systems carrying both voice and data comprise communication systems conforming to the “3rd Generation Partnership Project” (3GPP), embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), or “TR-45.5 Physical Layer Standard for cdma2000 Spread Spectrum Systems” (the IS-2000 standard).
An example of a data only communication system is a high data rate (HDR) communication system that conforms to the TIA/EIA/TIA/EIA/IS-895 industry standard, hereinafter referred to as the TIA/EIA/IS-895 standard. This HDR system is based on a communication system disclosed in co-pending application serial number 08/963,386, entitled “METHOD AND APPARATUS FOR HIGH RATE PACKET DATA TRANSMISSION,” filed Oct. 3, 1997, assigned to the assignee of the present invention. The HDR communication system defines a set of data rates, ranging from 38.4 kbps to 2.4 Mbps, at which an access point (AP) may send data to a subscriber station (access terminal, AT). Because the AP is analogous to a base station, the terminology with respect to cells and sectors is the same as with respect to voice systems.
Existing voice/data communication systems generally utilize voice traffic channels for conducting voice telephony or data communications including small file transfer, electronic mail, and facsimile. Consequently, the data transmission rate is limited. For example, in the above-mentioned communication system in accordance with the TIA/EIA/IS-95 standard provides for establishing multiple traffic channels, each having a rate of data up to 14.4 kilobits per second. While 14.4 kilobits per second is adequate for the above-mentioned types of lower data rate applications, the increasing popularity of more data intensive applications such as worldwide web and video conferencing has created a demand for much higher data transmission rates. The communication system in accordance with the TIA/EIA/IS-895 standard satisfies the data rate requirement, but allows for data transmission only. To satisfy the demand for data transmission while retaining voice service capability, several communication systems have been proposed.
One such a communication system is the above mentioned communication system in accordance with the W-CDMA standard. Another communication system is described in a proposal submitted by LG Electronics, LSI Logic, Lucent Technologies, Nortel Networks, QUALCOMM Incorporated, and Samsung to the 3rd Generation Partnership Project 2 (3GPP2). The proposal is detailed in documents entitled “Updated Joint Physical Layer Proposal for 1xEV-DV,” submitted to 3GPP2 as document number C50-20010611-009, Jun. 11, 2001, and “Updated Joint Physical Layer Proposal for 1xEV-DV,” file L3NQS_Physical_Layer_v09.doc, Aug. 20, 2001, hereinafter referred to as 1xEV-DV proposal. Yet another communication system is described in a proposal to the 3GPP2 submitted by Motorola, Nokia, Texas Instruments, and LSI Logic. The proposal is detailed in document entitled “1XTREME Physical Layer Specification for Integrated Data and Voice Services in cdma2000 Spread Spectrum Systems,” submitted to 3GPP2 as document number C50-20001204-021, Dec. 8, 2000.
The 1xEV-DV proposal provides an air interface between a plurality of subscriber stations and a plurality of subscriber stations enabling a simultaneous voice and data services. For that purpose, the 1xEV-DV proposal defines a set of forward and reverse channels.
The structure of reverse channels transmitted by base stations is illustrated in FIG. 1. The reverse Pilot Channel, the Dedicated Control Channel, and the Fundamental Channel remain unchanged. The Supplemental Channel structure remains unchanged for Radio Configurations 1 through 6. The new reverse control channels are the Reverse Rate Indicator Channel (R-RICH), the Reverse Channel Quality Indicator Channel (R-CQICH), and the Reverse Acknowledgment Channel (R-ACKCH).
The structure of forward channels transmitted by base stations is illustrated in FIG. 2. The Forward Pilot Channel, Transmit Diversity Pilot Channel, Auxiliary Pilot Channel, Auxiliary Transmit Diversity Pilot Channel, Synch Channel, Paging Channel, Broadcast Control Channel, Quick Paging Channel, Common Power Control Channel, Common Assignment Channel, Dedicated Control Channel, Forward Fundamental Channel, Forward Supplemental Channel, and Forward Supplemental Code Channels are the same as their counterparts in the above-mentioned IS-2000 standard. The Forward Packet Data Channel, the optional Forward Primary Packet Data Control Channel, and the Forward Secondary Packet Data Control Channel are channels defined for 1xEV-DV packet data operation.
The data services are provided to a subscriber station on a Forward Packet Data Channel (F-PDCH), which is shared by packet data users based on time multiplexing. The F-PDCH is composed of a number of code-division-multiplexed Walsh sub-channels. The number of sub-channels varies in time depending on the demands of the circuit-switched voice and data users. The F-PDCH structure is illustrated in FIG. 3. The information bit stream 302 to be transmitted is segmented into packets of several sizes. A 16-bit cyclic redundancy check (CRC) is added to each packet in block 304, and 6-bit turbo encoder tail allowance is added in block 306 yielding an encoder packet. In one embodiment, the encoder packets are of sizes 384 bits, 768 bits, 1,536 bits, 2,304 bits, 3,072 bits, and 3,840 bits. The encoder packets are encoded by block 308. Each encoded packet is then scrambled in blocks 310 by a scrambling pattern generated by block 312 and interleaved by block 314. Some or all of the interleaved symbols are then selected to form sub-packets in block 316. Depending on the length of the sub-packet, the sub-packet comprises 1, 2, 4, or 8 slots. In one embodiment, the slot is 1.25 ms long. The sub-packet are QPSK, 8-PSK, or 16-QAM modulated by block 318 and demultiplexed into a variable number of pairs (In-phase and Quadrature) of parallel streams by block 320. Each of the parallel streams is covered with a distinct 32-ary Walsh function by blocks 322(i). The Walsh-coded symbols of all the streams are summed together to form a single In-phase stream and a single Quadrature stream by block 324. The In-phase stream and the Quadrature streams are provided to a block 326, which adjusts the channel's gain. Several forward link channels, both data and voice are then summed in block 328, quadtrature spread in block 330, and the resultant In-phase and Quadrature streams are baseband filtered in block 332(i), upconverted in blocks 334(i) and summed in block 336.
The F-PDCH is controlled by a Forward Primary Packet Data Control Channel (F-PPDCCH) if used and by a Forward Secondary Packet Data Control Channel (F-SPDCCH).
The F-PPDCCH is transmitted during the first slot of F-PDCH transmissions, and carries a 2-bit field that indicates the F-PDCH sub-packet length. One of ordinary skills in the art recognizes that because the F-PPDCCH carries only information of the F-PDCH sub-packet length, the use of the F-PPDCCH is optional. The subscriber station may use other means for determining the F-PDCH sub-packet length. Thus, for example, the subscriber station may decode the sub-packet for all sub-packet length hypotheses, and select the most likely one of the hypothesis.
The F-SPDCCH is transmitted over 1, 2, or 4 slots, and the starts of the F-SPDCCH transmissions are aligned with the starts of the corresponding F-PDCH transmissions. The F-SPDCCH carries bits specifying a medium access control (MAC) identifier (ID), the Automatic Repeat reQuest (ARQ) channel ID, the encoder packet size, and the F-PDCH sub-packet ID.
The 1xEV-DV proposal thus allows the base station to send data to multiple mobiles only on a single slot granularity. Furthermore, the highest sub-packet data rate that is allowed for 384-bit packets is 307.2 kbps with one slot per sub-packet. So even when mobiles are capable of receiving higher data rates, they are limited to at most 307.2 kbps and use at least one slot.
Similarly, the 1XTREME proposal provides an air interface between a plurality of subscriber stations and a plurality of subscriber stations enabling a simultaneous voice and data services. The 1XTREME proposal uses a fixed sub-packet size of 5 ms for the packet data channels and for the control channels associated with the packet data channels. The packet data sub-packets can be CDM shared, but there is no flexibility on the duration of the data or control sub-packets. The packet data channel is controlled with a dedicated CDM channel for each user, called the Forward Dedicated Pointer Channel, and with a shared control channel, called the Forward Shared Control Channel.
The fixed-duration shared packet data sub-packet and limited control of the 1XTREME or 1xEV-DV proposals waste resources and limits the system throughput performance. Consequently, there is a need in the art for a method and an apparatus for improving the throughput of the system by allowing multiple forward-link transmissions per a slot.